11 January 2014

Sherlock Holmes made deductions from negative evidence with regard to dogs that did not bark in the night. One wonders if we can draw similar inferences today.
When I came to Aberfeldy in November 1960 as locum for Dr Yellowlees, the haughs, all the way along the strath, were full of geese. Since 1997 we have lived here, and the geese have come in their hundreds every early November. This year in mid December one has to search for them. I did see some high flying skeins in late October, probably Pink footed geese on their way to the RSPB Vane Farm reserve, but I have had to search for greylags only finding a few near Dunfallandy, where usually there are  hundreds.
This absence of winter migrants is not solely related to geese. Normally in early autumn the winter thrushes, fieldfares and redwings, arrive for a short visit to strip the rowans before flying on to warmer weather in England. Then they return as they move north again in spring when they can be seen in late February and early March. This year they, too, were late to arrive and are still here as I write in mid December. The whooper swans were late this year too as are most of the winter duck such as pochard, goldeneye and wigeon. By now Loch Kinardochy, when not frozen over, usually has plenty of activity as does Lochs Dunfallandy and the little reedy Loch-an-Darbh between them. Loch Freuchie too, normally alive with wildfowl has been unusually quiet - but then Glen Quaich (one of my favourite birding places) is being brutalised for the Beaulie Denny Line. Although this line of pylon construction is probably disrupting migration patterns across Highland Perthshire it cannot wholly account for the observed absence of geese and other wildfowl and it is necessary to look further.
David Attenborough in his programme Frozen Planet has urged on us the rapidity of Arctic warming. It seems logical to associate this with the absence or late arrival of winter birds. After all if it’s warmer up north why bother to fly south?  However this is difficult to relate to the ability of birds to time their migrations with the intensity of light and its daily variation in length. They do this by assessing light transmitted through their paper-thin skulls and using its changes as an extremely accurate clock (even blind birds know when to migrate). This assessment of diurnal length is what the warblers and swallows do when they arrive on cue in the spring. However even here temperature has its effect; swallows arriving in southern England in spring follow the isotherms as they move north.
All this pondering, as I search icy lochs for winter migrants, gets me no further in my thinking on climate change. Rationally I believe the science but our last two summers make it hard to believe we are all getting warmer. Perhaps the birds really are telling us something; if they are right we are in for far greater ecological changes than those produced by the Beaulie Denny Line.  
Though I am more Watson than Holmes I think even the great man himself might be surprised at the silence of pointing dogs.

Robin Hull


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